Heat-treatment oil composition

ABSTRACT

Provided is a heat-treatment oil composition that makes it possible to suppress quenching distortion and distortion variation and to achieve improved quenching hardness. A heat-treatment oil composition that includes a base oil (A) and a vapor film rupturing agent (B). The heat-treatment oil composition makes it such that, on a cooling curve obtained in accordance with the cooling performance test method in HS K2242:2012, the time in seconds to 300° C., e.g., the cooling time from 800° C. to 300° C., is at least 6.5 seconds but less than 10 seconds. Component (B) includes a petroleum resin.

TECHNICAL FIELD

The present invention relates to a heat-treatment oil composition.

BACKGROUND ART

A metal material such as a steel material is subjected to a heat treatment such as quenching, tempering, annealing and normalizing for the purpose of improving properties thereof. Among these heat treatments, quenching is a treatment for transforming a heated metal material to a predetermined quenched structure by immersing the metal material in a cooling medium, and this quenching makes the treated product very hard. For example, when a heated steel material in an austenite state is cooled at the upper critical rate or higher by immersing in a cooling medium, the material can be transformed to a quenched structure such as martensite.

As the cooling medium, an oil-based or water-based heat treatment agent is generally used. Quenching of a metal material using an oil-based heat treatment agent (heat treatment oil) will be described. When a heated metal material is put into a heat treatment oil serving as a cooling medium, the material is usually cooled through three stages. Specifically, the stages are: (1) the first stage where the metal material is enclosed with a vapor film of the heat treatment oil (vapor film stage); (2) the second stage where the vapor film is ruptured and boiling occurs (boiling stage); and (3) the third stage where the temperature of the metal material becomes the boiling point of the heat treatment oil or lower, and the heat is removed through convection (convection stage). The cooling rates in the stages are different from each other due to the difference of the atmosphere surrounding the metal material, and the cooling rate in the second stage (boiling stage) is the highest.

In a heat treatment oil, the cooling rate is generally increased quickly in the transition from the vapor film stage to the boiling stage. In the case where the metal material does not have a simple flat shape, the vapor film stage and the boiling stage tend to be mixedly present on the surface of the metal material. In the case where the stages are mixedly present, an extremely large temperature difference occurs on the surface of the metal material due to the difference in cooling rate between the vapor film stage and the boiling stage. The temperature difference generates thermal stress and transformation stress to cause distortion of the metal material. Therefore, in a heat treatment of a metal material, particularly quenching thereof, it is important to select a heat treatment oil appropriate for the heat treatment conditions, and if the selection is inappropriate, there may be a case where distortion occurs in the metal material and sufficient quenching hardness cannot be obtained.

Heat treatment oils are classified into Classes 1 to 3 according to JIS K2242:2012, and No. 1 oil and No. 2 oil of Class 1 and No. 1 oil and No. 2 oil of Class 2 are used for quenching.

JIS K2242:2012 determines the number of seconds for cooling from 800° C. to 400° C. as an index of cooling performance, and it is determined that the number of seconds is 5.0 seconds or less for No. 1 oil of Class 1, 4.0 seconds or less for No. 2 oil of Class 1, 5.0 seconds or less for No. 1 oil of Class 2, and 6.0 seconds or less for No. 2 oil of Class 2. The smaller the number of seconds for cooling is, the higher the cooling performance is, and the more the hardness of the metal material is increased. In general, the hardness and the distortion of the metal after quenching are in a trade-off relationship, and the higher the hardness is, the larger the distortion is.

As an industrial index of coolability of an oil, the number of seconds to 300° C. is also used. The number of seconds to 300° C. is a cooling time from 800° C. to 300° C. on a cooling curve that is obtained in accordance with the cooling performance test method of JIS K2242:2012.

As an index of coolability of an oil, the number of seconds until the temperature at which the vapor film stage ends (characteristic temperature) is reached from the start of the stage (characteristic number of seconds; vapor film length) is also used. In general, when the vapor film stage is prolonged, the period of time where the vapor film stage and the boiling stage are mixedly present is also prolonged, and it tends to increase the distortion. It is considered that higher coolability is obtained when the characteristic number of seconds is smaller and the characteristic temperature is lower. JIS K 2242:2012 also determines the characteristic temperature, and it is determined that the characteristic temperature is 480° C. or higher for No. 1 oil of Class 1, 580° C. or higher for No. 2 oil of Class 1, 500° C. or higher for No. 1 oil of Class 2, and 600° C. or higher for No. 2 oil of Class 2. No. 1 oil and No. 2 oil of Class 1 correspond to a cold oil that is used at a low oil temperature, No. 1 oil of Class 2 corresponds to a semi-hot oil that can be used at an oil temperature higher than that, and No. 2 oil of Class 2 corresponds to a hot oil that can be used at a high oil temperature.

A user selects a quenching oil based on the above-described indices for obtaining desired hardness and distortion. For example, for quenching an automobile gear component or the like where distortion may be problematic, the above-described No. 1 oil of Class 2 is widely used. This is because the above-described oils of Class 1 cause large distortion and may increase the hardness excessively for some components, and the above-described No. 2 oil of Class 2 causes small distortion, but provides insufficient hardness.

Components of a transmission and a speed reducer for an automobile, etc. are mass-produced in most cases, in which a large number of components to be treated are stacked on one tray and are quenched all at one time, that is, mass quenching is performed. In this case, there may be a problem that unevenness of hardness and distortion for respective stacked components is caused because unevenness of cooling performance is caused depending on the positions at which the components are set. For example, a component set at a lower position has higher hardness, and a component set at a higher position has lower hardness. In view of the above-described circumstances, the techniques of Patent Documents 1-4 have been proposed.

Patent Document 1 proposes a heat-treatment oil composition that reduces unevenness of cooling performance during mass quenching while having cooling performance equivalent to that of the above-described No. 1 oil of Class 2. Specifically, the heat-treatment oil composition contains a mixed base oil consisting of 5% by mass or more but less than 50% by mass of a low boiling point base oil having a 5% distillation temperature of 300° C. to 400° C. and more than 50% by mass but 95% or less of a high boiling point base oil having a 5% distillation temperature of 500° C. or higher.

Patent Document 2 proposes a heat-treatment oil composition that can reduce unevenness of cooling performance during mass quenching, wherein 50% by mass to 95% by mass of a base oil having a kinetic viscosity at 40° C. of 5 mm²/s to 60 mm²/s based on the total amount of the composition, 5% by mass to 50% by mass of a base oil having a kinetic viscosity at 40° C. of 300 mm²/s or more based on the total amount of the composition, and an α-olefin copolymer are blended.

Patent Document 3 proposes a heat-treatment oil composition that reduces unevenness of cooling performance during mass quenching while having cooling performance equivalent to that of the above-described No. 1 oil of Class 2, wherein: the composition comprises a petroleum resin as a vapor film rupturing agent; the characteristic number of seconds is 1.00 second or less; and the number of seconds to 300° C. is 6.00 seconds to 14.50 seconds.

Patent Document 4 proposes a heat-treatment oil composition that can exert high cooling performance, wherein a base oil having a kinetic viscosity at 40° C. of 4 mm²/s to 20 mm²/s and alkenyl or alkyl succinimide are blended.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Laid-Open Patent Publication No. 2007-009238

Patent Document 2: Japanese Laid-Open Patent Publication No. 2013-194262

Patent Document 3: Japanese Laid-Open Patent Publication No. 2016-151054

Patent Document 4: Japanese Laid-Open Patent Publication No. 2010-229479

SUMMARY OF THE INVENTION

It is desired to develop a heat-treatment oil composition having a good balance between cooling performance, quenching hardness and quenching distortion.

The present invention is as described below.

[1] A heat-treatment oil composition comprising a base oil (A) and a vapor film rupturing agent (B), wherein, on a cooling curve obtained in accordance with the cooling performance test method of JIS K2242:2012, the number of seconds to 300° C., which is the cooling time from 800° C. to 300° C., is 6.5 seconds or more but less than 10 seconds, and wherein the component (B) comprises a petroleum resin. [2] The heat-treatment oil composition according to item [1], wherein the characteristic number of seconds obtained from the cooling curve is 1 second or more. [3] The heat-treatment oil composition according to item [1] or [2], which further comprises a metal-based detergent dispersant (C). [4] The heat-treatment oil composition according to item [3], wherein the content of the component (C) is 0.01 to 10% by mass based on the total amount of the composition. [5] The heat-treatment oil composition according to any one of items [1] to [4], wherein the characteristic number of seconds obtained from the cooling curve is 2.5 seconds or less. [6] The heat-treatment oil composition according to any one of items [1] to [5], wherein the petroleum resin has a softening point of 40 to 150° C. [7] The heat-treatment oil composition according to any one of items [1] to [6], wherein the petroleum resin has a number-average molecular weight (Mn) of 200 to 5,000. [8] The heat-treatment oil composition according to any one of items [1] to [7], wherein the petroleum resin is a resin obtained by polymerizing or copolymerizing at least one unsaturated compound selected from an aliphatic olefin having 4 to 10 carbon atoms, an aliphatic diolefin, and an aromatic compound having an olefinic unsaturated bond and having 8 or more carbon atoms. [9] The heat-treatment oil composition according to any one of items [1] to [8], wherein the petroleum resin is at least one selected from an aliphatic petroleum resin, an aromatic petroleum resin, an aliphatic-aromatic copolymerization-based petroleum resin, a dicyclopentadiene-based petroleum resin, a dicyclopentadiene-aromatic copolymerization-based petroleum resin, and a hydrogenated petroleum resin and modified petroleum resin thereof. [10] The heat-treatment oil composition according to any one of items [1] to [9], which has a kinetic viscosity at 40° C. of 10 to 280 mm²/s. [11] The heat-treatment oil composition according to any one of items [1] to [10], wherein the component (A) comprises a low-viscosity base oil having a kinetic viscosity at 40° C. of 1 mm²/s or more but less than 85 mm²/s and a high-viscosity base oil having a kinetic viscosity at 40° C. of 85 to 550 mm²/s. [12] The heat-treatment oil composition according to any one of items [1] to [11], wherein the content of the petroleum resin is 0.1 to 90% by mass based on the total amount of the composition. [13] The heat-treatment oil composition according to any one of items [1] to [12], wherein the content of the component (A) is 10 to 99.9% by mass based on the total amount of the composition. [14] A method for quenching a metal material, wherein the metal material is treated with the heat-treatment oil composition according to any one of items [1] to [13]. [15] A method for producing the heat-treatment oil composition according to any one of items [1] to [13], which includes mixing the component (A) and the component (B).

According to the present invention, a heat-treatment oil composition having a good balance between cooling performance, quenching hardness and quenching distortion is provided.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the below-described embodiments and can be arbitrarily changed and then carried out without departing from the gist of the present invention.

The present invention relates to a heat-treatment oil composition comprising a base oil (A) and a vapor film rupturing agent (B). Regarding the heat-treatment oil composition of the present invention, on a cooling curve obtained in accordance with the cooling performance test method of JIS K2242:2012, the number of seconds to 300° C., which is the cooling time from 800° C. to 300° C., is 6.5 seconds or more but less than 10 seconds, and the component (B) comprises a petroleum resin.

The heat-treatment oil composition of the present invention has an excellent balance between cooling performance, quenching hardness and quenching distortion.

In the case of the heat-treatment oil compositions described in Patent Documents 1-3 (Japanese Laid-Open Patent Publication No. 2007-009238, Japanese Laid-Open Patent Publication No. 2013-194262, Japanese Laid-Open Patent Publication No. 2016-151054), the cooling time is long, quenching distortion is reduced, but quenching hardness may be insufficient for being applied to transportation components such as automobile components (e.g., gears and bearings), etc., and it is desired to further increase the hardness. Meanwhile, in the case of the heat-treatment oil composition described in Patent Document 4 (Japanese Laid-Open Patent Publication No. 2010-229479), the cooling time is short, quenching hardness is high, but quenching distortion is large, and it is difficult to apply the composition to a component having a complicated shape and the like. Accordingly, it is still desired to develop a heat-treatment oil composition, which can achieve a balance between high quenching hardness, reduced quenching distortion and unevenness of distortion, and which can be used for mass quenching of components.

According to a preferred embodiment, the heat-treatment oil composition can suppress quenching distortion and unevenness of distortion while achieving improved quenching hardness. The heat-treatment oil composition of the embodiment can be suitably used for mass quenching of components because quenching distortion and unevenness of distortion are suppressed by the composition. The heat-treatment oil composition of the embodiment can be suitably used for transportation components such as automobile components (e.g., gears and bearings), in particular, for small components.

Hereinafter, respective components will be described in detail. The upper limits and the lower limits of the numerical ranges described in this specification can be arbitrarily combined. For example, when “A to B” and “C to D” are described, ranges “A to D” and “C to B” are also included in the present invention. Further, the numerical range “the lower limit to the upper limit” described in this specification means the lower limit or more but the upper limit or less.

[Component (A): Base Oil]

The base oil is not particularly limited, and any material may be suitably selected from among mineral oils and synthetic oils which are conventionally used as a base oil of a heat-treatment oil.

Examples of mineral oils include: a paraffin group-based mineral oil, an intermediate group-based mineral oil and a naphthene group-based mineral oil, which are obtained by an usual purification method such as solvent purification and hydrogenation purification; and materials produced by isomerization of a wax produced by the Fischer-Tropsch process or the like (gas-to-liquid wax) or a mineral oil-based wax. These mineral oils may be used solely, or two or more of them may be used in combination.

Mineral oils are classified into Group I, II or III of the base oil category of API (The American Petroleum Institute). Mineral oils classified into Group II or III of the base oil category are preferred, and mineral oils classified into Group III are more preferred.

Examples of synthetic oils include a hydrocarbon-based synthetic oil and an ether-based synthetic oil. Examples of the hydrocarbon-based synthetic oil include alkylbenzene and alkylnaphthalene. Examples of the ether-based synthetic oil include polyoxyalkylene glycol and polyphenyl ether. These synthetic oils may be used solely, or two or more of them may be used in combination.

Further, at least one of the aforementioned mineral oils may be combined with at least one of the aforementioned synthetic oils to be used as the base oil.

The viscosity of the base oil is not particularly limited. The kinetic viscosity of the base oil at 40° C. is preferably 40 to 500 mm²/s, more preferably 50 to 350 mm²/s, even more preferably 60 to 200 mm²/s, and particularly preferably 80 to 120 mm²/s. By setting the kinetic viscosity of the base oil at 40° C. within the above-described range, essential cooling performance based on the component (A) can be ensured, while the characteristic number of seconds and the number of seconds to 300° C. can be easily adjusted to be within the below-described ranges.

Note that when the base oil of the component (A) is a base oil obtained by mixing two or more types of base oils, the kinetic viscosity of the mixed base oil is preferably within the above-described range.

In this specification, the kinetic viscosity at a predetermined temperature means a value obtained by the measurement in accordance with JIS K2283:2000.

The content of the base oil is preferably 10 to 99.9% by mass, more preferably 50 to 99% by mass, even more preferably 70 to 97% by mass, and particularly preferably 85 to 95% by mass based on the total amount of the composition.

In one embodiment of the present invention, the base oil comprises a low-viscosity base oil having a kinetic viscosity at 40° C. of 1 mm²/s or more but less than 85 mm²/s (more preferably 20 to 82 mm²/s, and even more preferably 40 to 80 mm²/s) and a high-viscosity base oil having a kinetic viscosity at 40° C. of 85 to 550 mm²/s (more preferably 88 to 520 mm²/s, and even more preferably 90 to 490 mm²/s).

Regarding blending of the low-viscosity base oil and the high-viscosity base oil in the mixed base oil, it is preferred that 0% by mass or more but less than 50% by mass (more preferably 3 to 30% by mass, and even more preferably 6 to 15% by mass) of the low-viscosity base oil and 50 to 99.9% by mass (more preferably 65 to 95% by mass, and even more preferably 80 to 90% by mass) of the high-viscosity base oil are contained in the heat-treatment oil composition based on the total amount of the composition.

In another embodiment of the present invention, the base oil comprises a low-viscosity base oil having a kinetic viscosity at 40° C. of 1 to 90 mm²/s (more preferably 20 to 82 mm²/s, and even more preferably 40 to 80 mm²/s) and a high-viscosity base oil having a kinetic viscosity at 40° C. of 90 to 500 mm²/s (more preferably 88 to 520 mm²/s, and even more preferably 90 to 490 mm²/s).

Regarding blending of the low-viscosity base oil and the high-viscosity base oil in the mixed base oil, it is preferred that 0% by mass or more but less than 50% by mass (more preferably 3 to 30% by mass, and even more preferably 6 to 15% by mass) of the low-viscosity base oil and 50 to 99.9% by mass (more preferably 65 to 95% by mass, and even more preferably 80 to 90% by mass) of the high-viscosity base oil are contained in the heat-treatment oil composition based on the total amount of the composition.

[Component (B): Vapor Film Rupturing Agent]

The heat-treatment oil composition comprises a petroleum resin as the vapor film rupturing agent. By using the petroleum resin, the vapor film stage can be shortened, and the vapor film stage and the boiling stage can be suppressed from being mixedly present on the surface of the metal material. Accordingly, the likelihood of the occurrence of uneven cooling performance (uneven hardness, uneven distortion) for respective components at the time of quenching can be lessened. Further, even when a component has a complicated shape, the likelihood of the occurrence of uneven cooling performance for respective portions of the component can be lessened, and therefore the distortion of each component can be suppressed. Moreover, when the petroleum resin is contained, the characteristic number of seconds at the initial stage of the heat treatment can be decreased, and accordingly, excellent cooling performance can be imparted from the initial stage of the heat treatment. In addition, by using the petroleum resin, when repeating the heat treatment of the metal material, the time-dependent change in cooling performance of the heat-treatment oil composition can be suppressed. Accordingly, by using the petroleum resin, the life of the heat-treatment oil composition can be prolonged. It is considered that the petroleum resin can exert these effects because of thermoplasticity thereof and excellent solubility thereof in the base oil.

The petroleum resin is a resin that is obtained through polymerization or copolymerization of one or at least two unsaturated compounds selected from among: an aliphatic olefin or aliphatic diolefin having 4 to 10 carbon atoms obtained as a by-product during the production of an olefin, such as ethylene obtained by thermal decomposition of a petroleum product such as naphtha; and an aromatic compound having an olefinic unsaturated bond and having 8 or more carbon atoms. For example, the petroleum resin is a resin obtained by copolymerization of dicyclopentadiene and an unsaturated compound including an aromatic compound, wherein the C5 fraction is used as the main raw material (dicyclopentadiene-aromatic copolymerization-based petroleum resin).

These petroleum resins can be roughly classified, for example, into an “aliphatic petroleum resin” obtained through polymerization of an aliphatic olefin and/or an aliphatic diolefin, an “aromatic petroleum resin” obtained through polymerization of an aromatic compound having an olefinic unsaturated bond, and an “aliphatic-aromatic copolymerization-based petroleum resin” obtained through copolymerization of an aliphatic olefin and/or an aliphatic diolefin and an aromatic compound having an olefinic unsaturated bond.

Examples of the aliphatic olefin having 4 to 10 carbon atoms include butene, pentene, hexene and heptene. Examples of the aliphatic diolefin having 4 to 10 carbon atoms include butadiene, pentadiene, isoprene, cyclopentadiene, dicyclopentadiene and methylpentadiene. Examples of the aromatic compound having an olefinic unsaturated bond and having 8 or more carbon atoms include styrene, α-methylstyrene, β-methylstyrene, vinyltoluene, vinylxylene, indene, methylindene and ethylindene.

The raw material compound of the petroleum resin is not required to be entirely a by-product during the production of an olefin by thermal decomposition of a petroleum product such as naphtha, and a chemically synthesized unsaturated compound may also be used. For example, a “dicyclopentadiene-based petroleum resin” obtained through polymerization of cyclopentadiene or dicyclopentadiene (DCPD), and a “dicyclopentadiene-aromatic copolymerization-based petroleum resin” obtained through copolymerization of cyclopentadiene or dicyclopentadiene and an aromatic compound having an olefinic unsaturated bond (e.g., dicyclopentadiene-styrene-based petroleum resin) can be used.

In this specification, the petroleum resin includes derivatives of the petroleum resin such as a hydrogenated petroleum resin and a modified petroleum resin.

The hydrogenated petroleum resin is obtained by adding hydrogen atoms to the aforementioned petroleum resin. By hydrogenation, all or a part of double bonds in the molecule are hydrogenated. Accordingly, the hydrogenated petroleum resin can be either a completely hydrogenated petroleum resin or a partially hydrogenated petroleum resin. When using a partially hydrogenated petroleum resin, the production is easily carried out because it has excellent coolability and a low softening point.

Examples of the modified petroleum resin include an acid-modified petroleum resin obtained through modification of the petroleum resin with an acidic functional group typified by a carboxylic acid, and a resin obtained through reaction modification of the acid-modified petroleum resin with a compound such as an alcohol, an amine, an alkali metal and an alkaline earth metal. Examples of the acid-modified petroleum resin include a carboxylic acid-modified petroleum resin and an acid anhydride-modified petroleum resin which are obtained through modification of the petroleum resin with an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride. Examples of the unsaturated carboxylic acid include an unsaturated monocarboxylic acid such as acrylic acid and methacrylic acid; an unsaturated polyvalent carboxylic acid such as maleic acid, fumaric acid, itaconic acid and citraconic acid; and a partial ester of an unsaturated polyvalent carboxylic acid such as monomethyl maleate and monoethyl fumarate, and examples of the unsaturated carboxylic acid anhydride include an unsaturated polyvalent carboxylic acid anhydride such as maleic anhydride and itaconic anhydride.

As the petroleum resin, a synthesized product may be used, or a commercially-available product may also be used.

Such petroleum resins may be used solely, or two or more of them may be used in combination.

In one embodiment, the petroleum resin is at least one selected from an aliphatic petroleum resin, an aromatic petroleum resin, an aliphatic-aromatic copolymerization-based petroleum resin, a dicyclopentadiene-based petroleum resin, a dicyclopentadiene-aromatic copolymerization-based petroleum resin, and a hydrogenated petroleum resin and modified petroleum resin thereof.

Among them, as the petroleum resin, an aliphatic-aromatic copolymerization petroleum resin and a hydrogenated aliphatic-aromatic copolymerization petroleum resin are preferred on the point that the characteristic number of seconds can be decreased, and a hydrogenated aliphatic-aromatic copolymerization petroleum resin is particularly preferred in view of the characteristic number of seconds. For example, the petroleum resin is a dicyclopentadiene-aromatic copolymerization-based hydrogenated petroleum resin.

The number-average molecular weight (Mn) of the petroleum resin is preferably 200 to 5000, more preferably 250 to 2500, and even more preferably 300 to 1500 from the viewpoint of the characteristic number of seconds. In this regard, the number-average molecular weight (Mn) can be measured by the VPO method.

The softening point of the petroleum resin is preferably 40° C. or higher, more preferably 40° C. to 150° C., even more preferably 60° C. to 150° C., still more preferably 80° C. to 140° C., still even more preferably 100° C. to 135° C., and particularly preferably 120° C. to 130° C. In this specification, the “softening point” can be measured by the ring-and-ball method of JIS K2207:2006. By setting the softening point at 40° C. or higher, the likelihood of the occurrence of uneven cooling performance (uneven hardness, uneven distortion) for respective components at the time of quenching can be more lessened, and in addition, when a component has a complicated shape, the likelihood of the occurrence of uneven cooling performance for respective portions of the component can be lessened, and the distortion of each component can be suppressed. Moreover, by setting the softening point at 40° C. or higher, the time-dependent change in cooling performance (the time-dependent increase in the characteristic number of seconds and the time-dependent reduction in the kinetic viscosity) at the time of repeating the heat treatment can be more suppressed, and the characteristic number of seconds at the initial stage of the heat treatment can be decreased. Further, by setting the softening point of the petroleum resin at 150° C. or lower, after cooling a material to be processed such as a metal material using the heat-treatment oil composition, stickiness on the surface of the processed material can be reduced. The softening point of the petroleum resin can be adjusted by the polymerization degree of the petroleum resin, a modified component and the modification degree thereof.

When using two or more types of materials as the petroleum resin, it is preferred that the softening points of all the materials are within the above-described range.

The density of the petroleum resin at 20° C. measured in accordance with JIS K 0061:2001 is preferably 0.5 to 1.5 g/cm³, more preferably 0.7 to 1.3 g/cm³, and even more preferably 0.8 to 1.1 g/cm³ from the viewpoint of cooling performance.

The bromine number of the petroleum resin is preferably 30 g/100 g or less, more preferably 20 g/100 g or less, and even more preferably 10 g/100 g or less from the viewpoint of cooling performance. Further, the lower the bromine number is, the better it is, and the lower limit thereof is not particularly limited, but it is usually 1.0 g/100 g or more, 1.5 g/100 g or more, or 1.9 g/100 g or more. In this regard, the bromine number is measured in accordance with JIS K 2605:1996.

Regarding the color phase of the petroleum resin, the Hazen color number measured in accordance with JIS K 6901:2008 is preferably 50 or less, more preferably 40 or less, and even more preferably 30 or less. Further, the lower the Hazen color number is, the better it is, and the lower limit thereof is not particularly limited, but it is usually 3 or more, 5 or more, or 7 or more.

The content of the petroleum resin is preferably 0.1 to 90% by mass based on the total amount of the composition. When the content is 0.1% by mass or more, cooling performance can be improved. The petroleum resin generally has a high viscosity, and there is a tendency that the larger the blending amount is, the higher the viscosity of the composition is. When the content is 90% by mass or less, it is preferred in view of an appropriate viscosity. The content of the petroleum resin is more preferably 1 to 60% by mass, and even more preferably 5 to 10% by mass from the viewpoint of the appropriate viscosity and cooling performance.

The heat-treatment oil composition may comprise an additional vapor film rupturing agent other than the petroleum resin. Examples of the additional vapor film rupturing agent include a terpene resin, a derivative of the terpene resin, rosin and a derivative of rosin. The content of the additional vapor film rupturing agent is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less based on the total amount of the composition. Particularly preferably, the heat-treatment oil composition does not comprise a vapor film rupturing agent other than the petroleum resin.

In one embodiment, the heat-treatment oil composition does not comprise an α-olefin copolymer as the vapor film rupturing agent.

In one embodiment, the heat-treatment oil composition does not comprise asphalt as the vapor film rupturing agent.

[Component (C): Metal-Based Detergent Dispersant]

The heat-treatment oil composition may comprise a metal-based detergent dispersant. When the metal-based detergent dispersant is contained, cooling performance can be improved. When the metal-based detergent dispersant (D) is contained together with the petroleum resin to be used as the vapor film rupturing agent (B), excellent cooling performance can be exerted, and the effect of further improving the hardness at the time of quenching is obtained.

Examples of the metal-based detergent dispersant (C) include an organic metal-based compound containing a metal atom selected from among an alkali metal atom and an alkaline earth metal atom (preferably an alkaline earth metal atom), and specific examples thereof include a metal salicylate, a metal phenate and a metal sulfonate. As the metal atom, a sodium atom, a calcium atom, a magnesium atom or a barium atom is preferred; a calcium atom or a magnesium atom is more preferred; and a calcium atom is even more preferred. Specifically, in one embodiment, the metal-based detergent dispersant (C) includes at least one of calcium salicylate, calcium phenate and calcium sulfonate. Such metal-based detergent dispersants may be used solely, or two or more of them may be used in combination.

The content of the metal-based detergent dispersant (C) is preferably 0 to 10% by mass, more preferably 0.1 to 7.5% by mass, and even more preferably 0.5 to 5% by mass based on the total amount of the composition. When the content is within the above-described range, it is preferred from the viewpoint of dispersibility in the base oil and excellent cooling performance.

[Component (D): Other Additives]

The heat-treatment oil composition may further comprise other additives including an antioxidant and a luster improving agent. The content of the other additives is preferably 10% by mass or less, and more preferably 0.01 to 5% by mass based on the composition.

(Antioxidant)

As the antioxidant, any material can be suitably selected from among publicly-known antioxidants which are conventionally used as antioxidants for heat-treatment oil compositions. Examples thereof include an amine-based antioxidant and a phenol-based antioxidant.

Examples of the amine-based antioxidant include: diphenylamine-based antioxidants such as diphenylamine and an alkylated diphenylamine having an alkyl group having 3 to 20 carbon atoms; and naphthylamine-based antioxidants such as α-naphthylamine and an alkyl-substituted phenyl-α-naphthylamine having 3 to 20 carbon atoms.

Examples of the phenol-based antioxidant include: monophenol-based antioxidants such as 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; diphenol-based antioxidants such as 4,4′-methylenebis(2,6-di-tert-butylphenol) and 2,2′-methylenebis(4-ethyl-6-tert-butylphenol); and hindered phenol-based antioxidants.

These antioxidants may be used solely, or two or more of them may be used in combination.

The content of the antioxidant is preferably 0.01 to 10% by mass, more preferably 0.03 to 5% by mass, and even more preferably 0.05 to 3% by mass based on the total amount of the composition.

(Luster Improving Agent)

When the luster improving agent is contained, it is possible to obtain good outer appearance of a material treated. Examples of the luster improving agent include oils and fats, fat fatty acids, alkenyl succinimide and a substituted hydroxy aromatic carboxylic acid ester derivative. These luster improving agents may be used solely, or two or more of them may be used in combination.

The content of the luster improving agent is preferably 0.01 to 5% by mass, and more preferably 0.02 to 3% by mass based on the total amount of the composition.

In one embodiment of the present invention, the total content of the base oil (A) and the vapor film rupturing agent (B) in the heat-treatment oil composition is preferably 80 to 100% by mass, more preferably 90 to 99.5% by mass, and particularly preferably 97 to 99% by mass based on the total amount of the composition (100% by mass).

In one embodiment of the present invention, the total content of the base oil (A), the vapor film rupturing agent (B) and the luster improving agent (C) in the heat-treatment oil composition is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, and particularly preferably 97.5 to 100% by mass based on the total amount of the composition (100% by mass).

[Physical Properties of Heat-Treatment Oil Composition]

Regarding the heat-treatment oil composition of the embodiment, it is required that, on a cooling curve obtained in accordance with the cooling performance test method of JIS K2242:2012, the “number of seconds to 300° C.”, i.e., the cooling time from 800° C. to 300° C., is 6.5 seconds or more but less than 10 seconds. From the viewpoint of the balance between quenching hardness, distortion and unevenness thereof, the number of seconds to 300° C. is more preferably 6.6 seconds to 9.5 seconds, and even more preferably 6.8 seconds to 9.2 seconds.

In order to set the number of seconds to 300° C. of the heat-treatment oil composition within the above-described range, the content and kinetic viscosity of the base oil (A), the content, softening point and number-average molecular weight of the vapor film rupturing agent (B) (particularly petroleum resin), and the content and structure of the metal-based detergent dispersant (C) are preferably set within the above-described ranges of the embodiment.

The heat-treatment oil composition having the number of seconds to 300° C. within the above-described range can be used as a heat-treatment oil (semi-hot oil) having cooling performance equivalent to that of No. 1 oil of Class 2 in JIS K2242:2012. The heat-treatment oil composition of the embodiment can realize suppression of unevenness of quenching distortion and high quenching hardness more when compared to conventional semi-hot oils.

Regarding the heat-treatment oil composition according to one embodiment, on a cooling curve obtained in accordance with the cooling performance test method of JIS K2242:2012, the “number of seconds to 400° C.”, i.e., the cooling time from 800° C. to 400° C., is preferably 2.0 to 4.5 seconds, more preferably 2.25 to 4.0 seconds, and even more preferably 2.3 to 3.5 seconds from the viewpoint of cooling performance.

Regarding the heat-treatment oil composition according to the embodiment, the characteristic number of seconds (vapor film length) obtained from a cooling curve obtained in accordance with the cooling performance test method of JIS K2242:2012 is preferably 1 second or more, more preferably 1.2 seconds or more, and particularly preferably 1.3 seconds or more from the viewpoint of reduction in distortion and reduction in unevenness thereof. Further, it is preferably 10 seconds or less, more preferably 5 seconds or less, and even more preferably 2.5 seconds or less from the viewpoint of reduction in unevenness of cooling performance for respective components at the time of quenching.

For example, the characteristic number of seconds (vapor film length) obtained from the cooling curve is 1 second to 10 seconds, 1 second to 5 seconds, 1 second to 2.5 seconds, 1.2 seconds to 10 seconds, 1.2 seconds to 5 seconds, 1.2 seconds to 2.5 seconds, 1.3 seconds to 10 seconds, 1.3 seconds to 5 seconds, or 1.3 seconds to 2.5 seconds.

In order to set the characteristic number of seconds of the heat-treatment oil composition within the above-described range, the content and kinetic viscosity of the base oil (A), the content, softening point and number-average molecular weight of the vapor film rupturing agent (B) (particularly petroleum resin), the content and structure of the metal-based detergent dispersant (C), etc. are preferably set within the above-described ranges of the embodiment.

The characteristic number of seconds can be more specifically calculated by the following procedures (1) and (2).

(1) In accordance with the cooling performance test method of JIS K2242:2012, a silver sample heated to 810° C. is put into the heat-treatment oil composition, and a cooling curve is obtained with the x-axis for the time and the y-axis for the temperature on the surface of the silver sample. (2) From the cooling curve, the number of seconds until the temperature at which the vapor film stage of the heat-treatment oil composition ends (characteristic temperature) is reached is calculated by the tangent crossover method, and the number of seconds is designated as the characteristic number of seconds.

In the procedure (1), the time interval of measurement is preferably 1/100 second.

The kinetic viscosity of the heat-treatment oil composition at 40° C. is preferably 10 to 280 mm²/s, more preferably 10 to 200 mm²/s, or more preferably 65 to 230 mm²/s, and even more preferably 115 to 180 mm²/s from the viewpoint of the number of seconds to 300° C.

The kinetic viscosity of the heat-treatment oil composition at 100° C. is preferably 1 to 40 mm²/s, more preferably 5 to 30 mm²/s, and even more preferably 10 to 20 mm²/s from the viewpoint of the number of seconds to 300° C.

[Method for Producing Heat-Treatment Oil Composition]

The method for producing the heat-treatment oil composition of the embodiment is not particularly limited. For example, the production method of the embodiment includes mixing the base oil (A) and the vapor film rupturing agent (B), and according to need, the metal-based detergent dispersant (C) and the other components (D). The components (A) to (D) may be blended by any method, and the order for blending and the technique thereof are not limited.

[Intended Use of Heat-Treatment Oil Composition, Quenching Method]

The heat-treatment oil composition of the embodiment can exert excellent cooling performance in the heat treatment of a metal material, and therefore can be suitably used, for example, as a heat-treatment oil for performing quenching of various alloy steels such as a carbon steel, a nickel-manganese steel, a chromium-molybdenum steel and a manganese steel. In particular, since the heat-treatment oil composition of the embodiment can achieve improved quenching hardness while suppressing quenching distortion, it can be suitably used, for example, as a quenching oil to be used for mass quenching of a gear such as a gear for automobiles, a metal material or the like.

The temperature of the heat-treatment oil composition of the embodiment at the time of performing a quenching treatment of a metal material using the composition may be set at a temperature within a range of 60 to 150° C. that is a usual temperature for the quenching treatment, or may be set at a high temperature within a range of 170 to 250° C.

One embodiment of the present invention provides a heat treatment method for a metal material. Specifically, the heat treatment method includes performing a heat treatment of a metal material using the heat-treatment oil composition of the above-described embodiment.

One embodiment of the present invention provides a quenching method for a metal material. Specifically, it is characterized in that the metal material is treated with the heat-treatment oil composition of the above-described embodiment. In a preferred embodiment, the quenching method for a metal material is characterized in that the metal material is treated with the heat-treatment oil composition of the above-described embodiment in mass quenching of the metal material. One embodiment of the present invention provides a mass quenching method for a metal material, which includes treating the metal material with the heat-treatment oil composition of the above-described embodiment.

In one embodiment, the quenching method for a metal material includes treating the metal material at an oil temperature of 60 to 200° C.

EXAMPLES

Hereinafter, the present invention will be described in detail by way of working examples, but the technical scope of the present invention is not limited thereto.

The measurement of physical properties of raw materials used in Examples and Comparative Examples and heat-treatment oil compositions in Examples and Comparative Examples was carried out according to points described below.

(1) Kinetic Viscosity

The kinetic viscosity at 40° C. and the kinetic viscosity at 100° C. were measured using a glass capillary viscometer in accordance with JIS K2283:2000.

(2) Cooling Performance of Heat-Treatment Oil Composition

In accordance with the cooling performance test method defined in JIS K2242:2012, a silver sample heated to 810° C. was put into the heat-treatment oil composition, a cooling curve of the silver sample was obtained, and the “characteristic number of seconds” and the “number of seconds to 300° C.” below were calculated. The oil temperature of the heat-treatment oil composition before the silver sample was put therein was 120° C. in all the Examples and Comparative Examples.

<Characteristic Number of Seconds and Characteristic Temperature>

On the cooling curve, in accordance with JIS K2242:2012, the temperature at which the vapor film stage ends (characteristic temperature) was calculated, and the number of seconds until the temperature was reached was designated as the characteristic number of seconds.

<Number of Seconds to 300° C.>

The cooling time from 800° C. to 300° C. on the cooling curve was designated as the number of seconds to 300° C.

<Number of Seconds to 400° C.>

The cooling time from 800° C. to 400° C. on the cooling curve was designated as the number of seconds to 400° C.

(3) Physical Properties of Petroleum Resin (i) Softening Point

The measurement was carried out in accordance with JIS K2207:2006.

(ii) Number-Average Molecular Weight (Mn)

The measurement was carried out by the VPO method.

(iii) Density

The density at 20° C. was measured in accordance with JIS K 0061:2001.

(iv) Color Phase

The Hazen color number was measured in accordance with JIS K 6901:2008.

(v) Bromine Number

The measurement was carried out in accordance with JIS K 2605:1996.

Examples 1-2, Comparative Examples 1-7

As shown in Table 1 below, components shown in Table 1 below were blended in a base oil to prepare each heat-treatment oil composition containing the base oil and the components in the Examples and Comparative Examples, and each heat-treatment oil composition prepared was evaluated with respect to hardness and distortion as described below. Characteristics and evaluation results of each heat-treatment oil composition in the Examples and Comparative Examples are shown in Table 1 below. The smaller the average ellipticity is, the smaller the quenching distortion is. The smaller the ellipticity 3a is, the smaller the unevenness of quenching distortion is. The higher the average internal hardness is, the higher the quenching hardness is. The larger the values of the average effective hardened layer depth and the average internal hardness are, the higher the hardness of a treated product after quenching is, and it indicates that a heat-treatment oil has excellent cooling performance.

<Evaluation of Hardness and Distortion>

As a material for evaluating quenching, a case hardened steel having a cylindrical shape (outer diameter: 85 mm, height: 44 mm, thickness: 4 mm, material: chromium-molybdenum steel SCM415) was used. It was subjected to a heat treatment (mass quenching) or the like under the below-described conditions, and evaluation was made with respect to the below-described items.

<Conditions for Heat Treatment, Etc.>

Heat treatment conditions: carburizing process: 930° C.×150 min, carbon potential (CP)=1.1% by mass

Diffusion process: 930° C.×60 min, CP=0.8% by mass

Soaking process: 850° C.×20 min, CP=0.8% by mass

Oil cooling conditions: oil temperature: 120′C, oil cooling time: 10 min, agitation: 20 Hz

Tempering conditions: 180′C×60 min

Setting method: sword hanger type (quenching 8 pieces (4 pieces×2))

<Evaluation Items>

Average ellipticity (mm)

Ellipticity 3σ (mm)

Average internal hardness (1.5 mm inside quenched material, HV)

Average effective hardened layer depth (mm)

TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example 1 Example 2 Example 3 Composition Base oil Base oil 1 % by mass 9 10 2 Base oil 2 % by mass 9 Base oil 3 % by mass 80.5 88 Base oil 4 % by mass 83 Base oil 5 % by mass 23 Base oil 6 % by mass 70.2 Base oil 7 % by mass 88 Base oil 8 % by mass Base oil 9 % by mass Base oil 10 % by mass Base oil 11 % by mass Vapor Petroleum resin 1 % by mass 6 9 film Petroleum resin 2 % by mass rupturing α-olefin copolymer % by mass 1.5 agent Asphalt % by mass 12 Additive Metal-based detergent % by mass 2 1.5 2 2 Antioxidant % by mass 1 Luster improving agent % by mass 0.3 Total 100 100 100 100 100 Characteristics Kinetic viscosity at 40° C. of base oil mm²/s 92 111 111 53.6 14 of base oil Kinetic viscosity at 100° C. of base oil mm²/s 11.2 12.3 12.3 7.7 3.2 Characteristics Kinetic viscosity at 40° C. of composition mm²/s 123 172 107 67 18 of composition Kinetic viscosity at 100° C. of composition mm²/s 13.0 16.0 19.0 9.2 3.9 Characteristic number of seconds sec 2.23 1.39 2.28 2.99 2.15 (vapor film length) Characteristic temperature ° C. 615 660 600 585 620 Number of seconds to 400° C. sec 3.27 2.74 3.22 3.95 2.7 Number of seconds to 300° C. sec 6.89 9.16 6.54 8.47 5.55 Evaluation Average ellipticity mm 0.205 0.185 0.223 0.210 0.210 Ellipticity 3σ mm 0.079 0.173 0.220 0.180 0.198 Average effective hardened layer depth mm 1.0 1.1 1.1 1.1 1.0 Average internal hardness Hv 421 406 417 425 438 Comparative Comparative Comparative Comparative Example 4 Example 5 Example 6 Example 7 Composition Base oil Base oil 1 5 Base oil 2 Base oil 3 Base oil 4 Base oil 5 Base oil 6 Base oil 7 Base oil 8 90.3 Base oil 9 90 Base oil 10 91 Base oil 11 99.25 Vapor Petroleum resin 1 film Petroleum resin 2 10 rupturing α-olefin copolymer 3 8 agent Asphalt Additive Metal-based detergent Antioxidant 1 0.75 Luster improving agent 1.7 Total 100 100 100 100 Characteristics Kinetic viscosity at 40° C. of base oil 23 120 60 200 of base oil Kinetic viscosity at 100° C. of base oil 4.5 13.4 8.3 18.0 Characteristics Kinetic viscosity at 40° C. of composition 31 — — — of composition Kinetic viscosity at 100° C. of composition 5.6 18.0 17.4 18.5 Characteristic number of seconds 1.92 0.89 0.53 1.58 (vapor film length) Characteristic temperature 648 700 720 645 Number of seconds to 400° C. 2.72 4.69 3.82 4.94 Number of seconds to 300° C. 6.24 10.73 11.08 10.76 Evaluation Average ellipticity 0.222 0.120 0.170 0.197 Ellipticity 3σ 0.263 0.142 0.174 0.240 Average effective hardened layer depth 1.0 0.9 0.9 0.9 Average internal hardness 430 346 322 328

The components used in Table 1 are as described below.

1. Base Oil (Component (A))

Base oil 1: paraffin-based mineral oil (kinetic viscosity at 40° C.: 480 mm²/s) (high-viscosity base oil) Base oil 2: paraffin-based mineral oil (kinetic viscosity at 40° C.: 75 mm²/s) (low-viscosity base oil) Base oil 3: paraffin-based mineral oil (kinetic viscosity at 40° C.: 97 mm²/s) (high-viscosity base oil) Base oil 4: paraffin-based mineral oil (kinetic viscosity at 40° C.: 94 mm²/s) (high-viscosity base oil) Base oil 5: paraffin-based mineral oil (kinetic viscosity at 40° C.: 395 mm²/s) (high-viscosity base oil) Base oil 6: paraffin-based mineral oil (kinetic viscosity at 40° C.: 31 mm²/s) (low-viscosity base oil) Base oil 7: paraffin-based mineral oil (kinetic viscosity at 40° C.: 14 mm²/s) (low-viscosity base oil) Base oil 8: paraffin-based mineral oil (kinetic viscosity at 40° C.: 21 mm²/s) (low-viscosity base oil) Base oil 9: paraffin-based mineral oil (kinetic viscosity at 40° C.: 120 mm²/s) (high-viscosity base oil) Base oil 10: paraffin-based mineral oil (kinetic viscosity at 40° C.: 60 mm²/s) (low-viscosity base oil) Base oil 11: paraffin-based mineral oil (kinetic viscosity at 40° C.: 200 mm²/s) (high-viscosity base oil)

2. Vapor Film Rupturing Agent (Component (B))

Petroleum resin 1: completely hydrogenated aliphatic-aromatic copolymerization-based petroleum resin (dicyclopentadiene-aromatic copolymerization-based hydrogenated petroleum resin in which C5 fraction is used as the main raw material; softening point: 125° C., number-average molecular weight: 820, density at 20° C.: 1.03 g/cm³, color phase (Hazen color number): 20, bromine number: 2.5 g/100 g)

Petroleum resin 2: partially hydrogenated aliphatic-aromatic copolymerization-based petroleum resin (dicyclopentadiene-aromatic copolymerization-based hydrogenated petroleum resin in which C5 fraction is used as the main raw material; softening point: 110° C., number-average molecular weight: 760, density at 20° C.: 1.05 g/cm³, color phase (Hazen color number): 25, bromine number: 6 g/100 g) α-olefin copolymer: α-olefin copolymer having a kinetic viscosity at 100° C. of 2000 mm²/s

3. Additives

Metal-based detergent dispersant (Component (C)): calcium salicylate

Antioxidant: phenol-based antioxidant

Luster improving agent: fat fatty acid

As shown in Table 1, it was confirmed that the heat-treatment oil compositions of the Examples which comprise a petroleum resin as the vapor film rupturing agent (B), wherein the number of seconds to 300° C. is 6.5 seconds or more but less than 10 seconds, have an average internal hardness of 400 Hv or higher and an average effective hardened layer depth of 1.0 mm or more, and have small values of the average ellipticity (less than 0.21) and unevenness thereof (ellipticity 3σ of less than 0.18).

Meanwhile, in the case where the number of seconds to 300° C. is not within the range of 6.5 seconds or more but less than 10 seconds and/or no petroleum resin is contained, at least one or both of desired hardness and low distortion (average ellipticity, ellipticity 3σ) were not obtained. Specifically, in each of Comparative Examples 5-7 in which the number of seconds to 300° C. was more than 10 seconds, the average internal hardness was lower than 350 Hv. In Comparative Example 4 in which the number of seconds to 300° C. is less than 6.5 seconds and no petroleum resin is contained, and in Comparative Examples 1-2 in which no petroleum resin is contained, quenching distortion (in particular, unevenness of quenching distortion (ellipticity 3σ)) was large.

The scope of the present invention is not limited to the description above. In addition to the above-described examples, the present invention can be suitably changed and then practiced within a range in which the effects of the present invention are not reduced. Note that all the documents and publications cited herein are incorporated herein by reference in their entireties regardless of purposes thereof. In addition, the contents disclosed in the claims and specification of Japanese Patent Application No. 2018-062472 (filed on Mar. 28, 2018), to which priority is claimed by the present application, are incorporated herein.

INDUSTRIAL APPLICABILITY

The heat-treatment oil composition of the present invention can be suitably used at the time of performing a heat treatment such as quenching of a metal material. 

1. A heat-treatment oil composition, comprising: a base oil; and a vapor film rupturing agent comprising a petroleum resin, wherein, on a cooling curve obtained in accordance with a cooling performance test method of JIS K2242:2012, a number of seconds to 300° C., which is a cooling time from 800° C. to 300° C., is 6.5 seconds or more but less than 10 seconds.
 2. The heat-treatment oil composition according to claim 1, wherein a characteristic number of seconds obtained from the cooling curve is 1 second or more.
 3. The heat-treatment oil composition according to claim 1, further comprising: a metal-based detergent dispersant.
 4. The heat-treatment oil composition according to claim 3, wherein metal-based detergent dispersant is present in a range of from 0.01 to 10% by mass based on a total amount of the composition.
 5. The heat-treatment oil composition according to claim 1, wherein the characteristic number of seconds obtained from the cooling curve is 2.5 seconds or less.
 6. The heat-treatment oil composition according to claim 1, wherein the petroleum resin has a softening point of from 40 to 150° C.
 7. The heat-treatment oil composition according to claim 1, wherein the petroleum resin has a number-average molecular weight (Mn) of from 200 to 5,000.
 8. The heat-treatment oil composition according to claim 1, wherein the petroleum resin is a resin obtained by polymerizing or copolymerizing at least one unsaturated compound selected from the group consisting of an aliphatic olefin comprising from 4 to 10 carbon atoms, an aliphatic diolefin, and an aromatic compound having comprising an olefinic unsaturated bond and 8 or more carbon atoms.
 9. The heat-treatment oil composition according to claim 1, wherein the petroleum resin is at least one selected from the group consisting of an aliphatic petroleum resin, an aromatic petroleum resin, an aliphatic-aromatic copolymerization-based petroleum resin, a dicyclopentadiene-based petroleum resin, a dicyclopentadiene-aromatic copolymerization-based petroleum resin, and a hydrogenated petroleum resin and modified petroleum resin thereof.
 10. The heat-treatment oil composition according to claim 1, having a kinetic viscosity at 40° C. of from 10 to 280 mm²/s.
 11. The heat-treatment oil composition according to claim 1, wherein the base oil comprises a low-viscosity base oil having a kinetic viscosity at 40° C. of 1 mm²/s or more but less than 85 mm²/s and a high-viscosity base oil having a kinetic viscosity at 40° C. of from 85 to 550 mm²/s.
 12. The heat-treatment oil composition according to claim 1, wherein the petroleum resin is present in a range of from 0.1 to 90% by mass based on a total amount of the heat-treatment oil composition.
 13. The heat-treatment oil composition according to claim 1, wherein the base oil is present in a range of from 10 to 99.9% by mass based on a total amount of the heat-treatment oil composition.
 14. A method for quenching a metal material, the method comprising: treating the metal material with the heat-treatment oil composition according to claim
 1. 15. A method for producing the heat-treatment oil composition according to claim 1, the method comprising: mixing the base oil and the vapor film rupturing agent. 